Automated blood pressure monitoring has rapidly become an accepted and, in many cases, essential aspect of human and veterinary treatment. Such monitors are now a conventional part of the patient environment in emergency rooms, intensive and critical care units, and in the operating theatre.
The so-called oscillometric method of measuring blood pressure is one of the most popular methods in commercially available systems. This method relies on measuring changes in arterial counterpressure, such as imposed by an inflatable cuff, which is controllably relaxed or inflated. In some cases the cuff pressure change is continuous, and in others it is incremental. In substantially all, a transducer monitors arterial counterpressure oscillations, and processing apparatus converts select parameters of these oscillations into blood pressure data.
Of particular interest with respect to the principles of the present invention are the concepts set forth in U.S. Pat. Nos. 4,360,029 and 4,394,034 to M. Ramsey, III, which are commonly assigned with the instant invention. The Ramsey patents derive from common parentage, the former including apparatus claims and the latter including method claims, their division having been made in response to a restriction requirement during the prosecution. Both patents, however, carry common disclosures of apparatus and methods for artifact rejection in oscillometric systems, which have been in practice in the commercially successful DINAMAP brand monitors, which are manufactured and marketed by Critikon, Inc., of Tampa, Fla., the assignee hereof. In accordance with the Ramsey patents, an inflatable cuff is suitably located on the limb of a patient, and is pumped up to a predetermined pressure. Thereupon, the cuff pressure is reduced in predetermined fixed decrements, at each level of which pressure fluctuations are monitored. These typically consist of a DC voltage with a small superimposed variational component caused by arterial blood pressure pulsations (referred to herein as "oscillatory complexes"). Therefore, after suitable filtering to reject the DC component and to provide amplification, pulse peak amplitudes above a given threshold are measured and stored. As the decrementing continues, the peak amplitudes will normally increase from a lower amount to a relative maximum, and thereafter will decrease. The lowest cuff pressure at which the oscillations have a maximum peak value is representative of mean arterial pressure. The cuff pressures obtaining when stored oscillatory complex pulse peak amplitudes bear predetermined fractional relationships with the largest stored peak corresponding to the subject's systolic and diastolic pressures.
The Ramsey patents devote considerable effort and disclosure to the rejection of artifact data to derive accurate blood pressure data. Indeed, as is apparent from FIG. 2 of the Ramsey patents, the most substantial portion of the measurement cycle (denominated "T3") is devoted to the execution of complex detection at the various pressure levels, measurement of signal peaks of true complexes, and processing those peaks in accordance with artifact rejection algorithms. Notwithstanding such efforts, the signal peak data collected sometimes incorporates data errors, i.e., a data pattern inconsistent with the above described typical physiological response pattern of a subject as the artery occluding cuff pressure monotonically decreases.
Further, in a contemporaneous invention (see M. Ramsey III, et al patent application Ser. No. 751,840 for "OSCILLOMETRIC BLOOD PRESSURE MONITOR EMPLOYING NON-UNIFORM PRESSURE DECREMENTING STEPS" filed on even date herewith, the disclosure of which is incorporated herein by reference) oscillometric blood pressure measurements are effected with non-uniform, cuff pressure-dependent pressure decrements between successive oscillatory complex peak measuring intervals. Such a method of effecting oscillometric blood pressure measurements is facilitated by systolic, diastolic and mean blood pressure determining algorithms not heretofore employed.
It is an object of the present invention to provide improved oscillometric blood pressure determining apparatus and methodology.
More specifically, it is an object of the present invention to purify the oscillatory complex peak amplitude data ensemble employed for blood pressure determination.
Yet another object of the present invention is the provision of improved algorithms, methodology and apparatus for determining diastolic blood pressure.